Product category:
Plating and plating systems
News Release from: MacDermid | Subject: Non-chrome passivate
Edited by the Manufacturingtalk Editorial
Team on 24 January 2006
Meeting RoHS/WEEE/ELV compliance for Al
parts
Totally inorganic, non-chrome passivate, using the same application methods and parameters as the traditional yellow chromates, meets ROHS, WEEE and ELV directives.
Eliminating chrome from the workplace is part of a massive undertaking which will benefit both the environment and worker safety, and if done correctly should not increase the overall cost of your product Developed in 2002, Iridite NCP is a totally inorganic, non-chrome passivate (NCP) using the same application methods and parameters as the traditional yellow chromates
This article was originally published on Manufacturingtalk on 19 Nov 2007 at 8.00am (UK)
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Iridite NCP is believed to be the first chrome-free conversion coating for aluminium to be approved and listed in the EU Qualified Products List for the MIL-DTL-5541F specification.
The bath and resulting coating does not contain any banned components found within the ROHS, WEEE and ELV directives.
The chemistry is truly reactive, unlike the polymer based 'chrome free' paint pretreatments, so it can be completely rinsed after application thus extending bath life and performance.
Like the yellow chromate the Iridite NCP exhibits bare corrosion resistance without painting and also excellent paint adhesion characteristics.
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As the Iridite NCP application procedure is practically identical to the yellow hexavalent chromate, we have tested it head to head using a standard conversion coating process sequence.
* Corrosion resistance - using a standard ASTM B117 salt spray test on conversion coated panels, Iridite NCP gave in excess of 1000h on most 1000, 3000, 5000 and 6000 series alloys, giving a better overall performance than that obtained from the traditional yellow chromate.
The main cause of poor salt spray resistance in aluminium alloys is copper content, and copper levels above 2% greatly reduce salt spray life.
Chromate conversion coatings still outperform Iridite NCP when used on these alloys although even chromate has limited salt spray life on high copper alloys.
Due to their low inherent corrosion resistance high copper alloys are rarely used in applications requiring high corrosion resistance without painting or cladding, in which case Iridite NCP can still out-perform chrome based passivates.
When painted all of the Iridite NCP panels, regardless of alloy, passed >1128h salt spray with neither creep from scribe nor loss of adhesion with a cross hatch and tape pull test.
This confirms Iridite NCP is suitable for all alloys which require painting.
* Electrical resistivity - electrical chassis and enclosures are often made from chromated aluminium to allow electrical grounding whilst still providing corrosion resistance.
Iridite NCP will meet the MIL-C-81706 electrical resistivity test both before and after salt spray ensuring continued performance during service.
* Paintability - in order to accept paint properly the coating must be intrinsically hydrophilic so the surface wets out to allow the paint to flow.
This is measured by the contact angle of a water droplet on the surface.
A freshly applied Iridite NCP coating will have a contact angle of 80 compared to 110 for a new yellow chromate.
After aging the results become rather different, the Iridite NCP still remains hydrophilic measuring 390 where as the chromate becomes distinctly hydrophobic with a measurement of 650.
Other benefits - besides being a 'drop-in' replacement for chromates, Iridite NCP has other benefits, which can be utilised by the manufacturer and subcontractor: * Robustness of coating - a traditional yellow chromate coating forms as a soft gel on the metal surface, which is susceptible to damage and takes 24h to cure to a reasonably hard film.
If left in the tank the chromate will continue to build up, becoming lose, powdery and non adherent.
The Iridite NCP coating on the other hand, is self limiting, producing a hard amorphous coating as formed and does not require any curing time.
* Thermal stability - treatment of a chromated surface after it has formed is important for it to produce a corrosion resistant surface or a good paint bond.
Heating above 700 deg C will dehydrate and crack the chromate film.
Iridite NCP can be heated to 3500 deg C without any significant loss of corrosion protection or paint adhesion.
The coating does not dehydrate or crack.
This allows the use of hot water rinses and higher temperatures in dry off ovens prior to paint application, speeding up drying times and production.
Stability up to 3500 deg C offers the use of Iridite NCP for bare aluminium articles that see high operating temperatures in service, e g, automotive brake and engine components. Request a free brochure from MacDermid ...
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